1. Field of the Invention
The present invention relates to data communications; and particularly to communications operating with low power, and to integrated circuits including resources supporting such data communications.
2. Description of Related Art
The bulk of off-chip communication in modern digital signals occurs between chips on a single printed circuit board. Contemporary signaling solutions include low voltage CMOS (LVCMOS) described for example in JEDEC Standard No. 8-B (1999), high speed transceiver logic (HSTL) interfaces, described for example in JEDEC Standard No. 8-6 (1995), and high-speed serial links.
Signaling power required for communication dominates system power in many cases. A major consumer of power in the signaling system is driving the transmission line. Representative high-speed signaling systems drive transmission lines with 10–20 milliamps of current, resulting in differential signal swings of 500 millivolts to 1 volt at the transmitter on a 100 ohm line. Thus, the signal swings on contemporary communication lines consume considerable power (5–20 milliwatts from a 1 volt supply). Moreover, the large transmitters needed to drive such high currents present large clock loads, driving up the clock power required.
Higher signaling power is required for chip-to-chip communication, in part to establish signal-to-noise ratios on the communication channels that are high enough to meet rigorous bit error rate (BER) standards on the order of 10−9 or better. The typical signal swings, discussed above, are far greater than needed to overcome the fundamental noise sources in the system, such as thermal noise in the terminating resistors, that are normally in the microvolt range. However, fixed noise sources, like component imbalances, voltage offsets, cross-talk and some inter-symbol interference, have greater levels, and drive the requirements for signaling power up.
It is desirable to provide a high speed communication technology operable with low power, while meeting or exceeding BER standards.